Effect of indomethacin on responses of sheep isolated coronary artery to arachidonic acid.

Indomethacin (2.8 mumol/l) did not consistently affect basal tone of sheep coronary artery strips, while a ten-fold higher concentration increased tension in 50% of the preparations tested. When acetylcholine was used as a spasmogen, oscillations in induced tone and relaxations produced by arachidonic acid (6.6 mumol/l) were abolished by indomethacin, 2.8 mumol/l and 7 mumol/l, respectively. Prostacyclin (PGI2) and prostaglandin E1 decreased and PGE2 increased arterial tension while PGF2 alpha was inactive. Responses to PGI2 were reduced by indomethacin (28 mumol/l) but not by indomethacin (2.8 mumol/l). It is suggested that sheep isolated coronary arteries synthesize and release prostacyclin in the presence of acetylcholine and arachidonic acid and that such synthesis can be inhibited by indomethacin.